salvationfound voiced what I was waiting for a Christian to say. He or she wrote:

If someone wants to kill and they feel the advantages outweigh the disadvantages why shouldn't they kill?

I'm assuming here that sf is talking about a premeditated unlawful and unjust killing of another human being. My answer?

Under these circumstances then he will kill, because that's why people get murdered in the first place by others who kill them. Since I'm arguing that every human being is motivated to act from self-interest, then if these conditions obtain for someone, they will therefore kill. And it doesn't matter what a person's religious or non-religious beliefs are at that point, because these beliefs also factor into whether the advantages outweigh the disadvantages. Whether one is a Christian or not, people will kill under these circumstances.

There is no ethic that can stop someone from killing under these circumstances...none. Since Christianity numberically dominates in American society then a whole lot of Christians are killing other people. Men kill their wives. Women kill their husbands and children. Others kill while stealing. Men kill after raping a woman. Who do you think are doing most of the killing here? Christians. Why do they do this? Because the advantages outweigh the disadvantages. Some do so while in an irrational rage, or because of paranoia, or due to drugs or alcohol. But they do it. And so do atheists and agnostics.

Christians will say that the Christians who kill others are not "real Christians." What can we make of this? According to such a definition a Christian is someone who obeys the Bible? But how does that follow from the contrary idea that we cannot earn our way into heaven? How can they have it both ways? Deeds mean little to the evangelical mind in front of a merciful God. Evangelicals will claim there is no deed God cannot forgive, so murder should be no problem for God. Christians say a person must repent before he can be forgiven, but does that mean they can fall away from God's grace, or that their repentence must be perfect before God can forgive them? And does this mean they should search out every possible sin and daily repent of it before God will forgive? Surely not. Lewis B. Smedes [in his book Mere Morality] makes a strong case that God can and does forgive suicide, and there can be no repentence after such a deed is committed.

Christians can have an excuse whenever they want to do wrong. I know. As a former Christian I knew God would forgive me if I did something wrong. So, when I felt the advantages outweighed the disadvantages I did it knowing full well God would forgive me.

Having said all of this, I dispute the basis of the question sf asked. I claim that the advantages will never outweight the disadvantages in unlawfully and unjustly killing someone, period. Give me a scenario and I doubt that rational self-interest will ever conclude the right thing to do is to kill someone (except in self-defense). My position is that people who kill are not acting rationally.